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The Diagnostic and Prognostic Significance of CD45 Antigen in Acute Leukemia

CD45 or LCA (leukocyte common antigen) is transmembrane glycoprotein active as tyrosine kinase. It is expressed solely on precursor and mature hematopoietic cells. Its significance is derived in the possibility of differentiate between hematopoietic (CD45+) and nonhematopoietic (CD45-) tissue, especially in the context of the differential diagnosis between extranodal lymphomas and nodal and bone nonhematologic malignancies and their metastases. In the immunophenotyping of acute leukemia, CD45 is a biomarker used to distinguish the population of blasts, characterized by the expression of low CD45 antigen and moderate to high side scrater (SSC) parameter. The CD45 antigen immunophenotyping is currently defined and confirmed by numerous data in the detection of minimal residual disease (MRD) in acute lymphoblastic leukemia (ALL), especially in CD45 negative types. Also, its usage contributes to higher sensitivity of multiparametric flow cytometry in detecting MRD of acute myeloid leukemia (AML). Due to the variable expression of CD45RO and CD45RA isoforms during normal hematopoiesis, the expression of these isoforms on the blasts varies based on the type of AML and between B-cell and T-cell ALL. The subgroup of CD45 negative leukemias is defined by the expression of this antigen <20%. The prevalence varies between 12.9% and 14% among acute childhood leukemias. Due to the lack of data, it is estimated that prevalence amounts up to 11% among acute adulthood leukemia. Several studies have shown the prognostic significance of CD45 antigen in childhood ALL showing the correlation of low and lack of CD45 expression with other positive prognostic biomarkers and better treatment outcome. It seems that actual percentage of CD45 expression intensity has greater value as prognostic factor than simple subdivision in CD45 positive or negative leukemias. It has been shown that the high intensity (>75%) of CD45 and moderate (>20%) intensity of CD20 antigen are independent prognostic factors in ALL. Recent studies in childhood AML have described that the high percentage of CD34+/CD38-/CD45- blasts is associated with worse prognosis. Meanwhile, the research on CD45 antigen significance in adult forms of leukemia remains scarce. Only few papers have shown the possible positive prognostic features of CD45- negative ALL, while we have not been able to find the data on CD45 expression in AML. In our study, 128 patients suffering from acute leukemia were included. Ninety-seven (75.8%) patients were diagnosed with AML, 26 patients (20.3%) with ALL, four cases of biphenotypic leukemias (AML/ALL) and one case of undifferentiated leukemia were recorded. Only one cases in ALL subgroups was CD45 negative, while additional four cases had moderate CD45 expression intensity (<75%), accounting for 19.2% of ALL. In AML subgroup, all cases had CD45 antigen high expression intensity (>75%), with only six subjects having the CD45 intensity <90%. Based on our data, it seems that the prevalence of CD45 negative leukemia subgroup in adulthood is lower than in those in children. Due to the small number in this sample, we were not able to analyse further its prognostic significance.

CD45 antigen; acute leukemia

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